Pretreatment as the crucial step for biogas reforming over Ni–Co bimetallic catalyst – A mechanistic study of CO2 pretreatment

•A mechanistic study of H2 and CO2 pretreatment was investigated.•Ni was considered as the main metal that interacted with CO2.•H2 reduction is an indispensible step of the pretreatment route.•The bicarbonate of Ni was formed during the CO2 pretreatment.•The bicarbonate of Ni is the key to improve the performance of catalyst.

H2 and CO2 pretreatment over the Ni–Co/La2O3–Al2O3 catalyst has been shown to lead to significant increase in catalytic performance. A mechanistic study was investigated by a series of catalytic activity measurements. Ni was found to be the main metal that interacted with CO2. Meanwhile, H2 reduction is an indispensable step of the pretreatment route and CO2 cannot be replaced by O2. FT-IR spectroscopy investigations were used to confirm that carboxyl was created during the CO2 pretreatment of the Ni–Al2O3 catalyst. The result proved that bicarbonate of Ni was formed during the CO2 pretreatment. During CO2-reforming of methane, the bicarbonate of Ni could decompose into CO and provide oxygen species. The oxygen species will react with accumulated carbon on Ni crystallites to produce CO and in turn protect the active sites. Thus, the performance of the catalyst was significantly improved.